Biodegradable microcapsules prepared by a w/o/w technique: effects of shear force to make a primary w/o emulsion on their morphology and protein release

Protective Effect of IgY Embedded in W/O/W Emulsion on LPS Enteritis-Induced Colonic Injury in Mice

Chicken yolk immunoglobulin (IgY), an immunologically active component, is used as an alternative to antibiotics for the treatment of enteritis. In this study, IgY was embedded in a W/O/W emulsion to overcome the digestive barrier and to investigate the protective effect of IgY against LPS-induced enteritis in mice. Four different hydrophilic emulsifiers (T80, PC, SC, and WPI) were selected to prepare separate W/O/W emulsions for encapsulating IgY. The results showed that the IgY-embedded double emulsion in the WPI group was the most effective. IgY embedded in the W/O/W emulsion could reduce the damage of LPS to the mouse intestine and prevent LPS-induced intestinal mucosal damage in mice. It increased the number of cup cells, promoted the expression of Muc2, and increased the mRNA expression levels of KLF3, TFF3, Itln1, and Ang4 (p < 0.05). It also enhanced the antioxidant capacity of the colon tissue, reduced the level of inflammatory factors in the colon tissue, and protected the integrity of the colon tissue. Stable embedding of IgY could be achieved using the W/O/W emulsion. In addition, the IgY-embedded W/O/W emulsion can be used as a dietary supplement to protect against LPS-induced enteritis in mice.

Pharmaceutically modified subtilisins withstand acidic conditions and effectively degrade gluten in vivo

Detoxification of gluten immunogenic epitopes is a promising strategy for the treatment of celiac disease. Our previous studies have shown that these epitopes can be degraded in vitro by subtilisin enzymes derived from Rothia mucilaginosa, a natural microbial colonizer of the oral cavity. The challenge is that the enzyme is not optimally active under acidic conditions as encountered in the stomach. We therefore aimed to protect and maintain subtilisin-A enzyme activity by exploring two pharmaceutical modification techniques: PEGylation and Polylactic glycolic acid (PLGA) microencapsulation. PEGylation of subtilisin-A (Sub-A) was performed by attaching methoxypolyethylene glycol (mPEG, 5 kDa). The PEGylation protected subtilisin-A from autolysis at neutral pH. The PEGylated Sub-A (Sub-A-mPEG) was further encapsulated by PLGA. The microencapsulated Sub-A-mPEG-PLGA showed significantly increased protection against acid exposure in vitro. In vivo, gluten immunogenic epitopes were decreased by 60% in the stomach of mice fed with chow containing Sub-A-mPEG-PLGA (0.2 mg Sub-A/g chow) (n = 9) compared to 31.9% in mice fed with chow containing unmodified Sub-A (n = 9). These results show that the developed pharmaceutical modification can protect Sub-A from auto-digestion as well as from acid inactivation, thus rendering the enzyme more effective for applications in vivo.

Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone

Electrosprayed polycaprolactone (PCL) microparticles are widely used in medical tissueengineering, drug control release delivery, and food packaging due to their prominent structuresand properties. In electrospraying, the selection of a suitable solvent system as the carrier of PCL isfundamental and a prerequisite for the stabilization of electrospraying, and the control ofmorphology and structure of electrosprayed particles. The latter is not only critical for diversifyingthe characteristics of electrosprayed particles and achieving improvement in their properties, butalso promotes the efficiency of the process and deepens the applications of electrosprayed particlesin various fields. In order to make it systematic and more accessible, this review mainly concludesthe effects of different solution properties on the operating parameters in electrospraying on theformation of Taylor cone and the final structure as well as the morphology. Meanwhile,correlations between operating parameters and electrospraying stages are summarized as well.Finally, this review provides detailed guidance on the selection of a suitable solvent systemregarding the desired morphology, structure, and applications of PCL particles.

Fibrous Protein Self-Assembly in Biomimetic Materials

Protein self-assembly processes, by which polypeptides interact and independently form multimeric structures, lead to a wide array of different endpoints. Structures formed range from highly ordered molecular crystals to amorphous aggregates. Order arises in the system from a balance between many low-energy processes occurring due to a set of interactions between residues in a chain, between residues in different chains, and between solute and solvent. In Nature, self-assembling protein systems have evolved over millions of years to organize into supramolecular structures, optimized for specific functions, with this propensity determined by the sequence of their constituent amino acids, of which only 20 are encoded in DNA. The structural materials that arise from biological self-assembly can display remarkable mechanical properties, often as a result of hierarchical structure on the nano- and microscales, and much research has been devoted to mimicking and exploiting these properties for a variety of end uses. This work presents a review of a range of studies in which biological functions are effectively reproduced through the design of self-assembling fibrous protein systems.

Mechanistic studies for monodisperse exenatide-loaded PLGA microspheres prepared by different methods based on SPG membrane emulsification

Poly(DL-lactic-co-glycolic acid) (PLGA) microspheres have been widely prepared by many methods, including solvent evaporation, solvent extraction and the co-solvent method. However, very few studies have compared the properties of microspheres fabricated by these methods. This is partly because the broad size distribution of the resultant particles severely complicates the analysis and affects the reliability of the comparison. To this end, uniform-sized PLGA microspheres have been prepared by Shirasu porous glass premix membrane emulsification and used to encapsulate exenatide, a drug for treating Type 2 diabetes. Based on this technique, the influences on the properties of microspheres fabricated by the aforementioned three methods were intensively investigated, including in vitro release, degradation and pharmacology. We found that these microspheres presented totally different release behaviors in vitro and in vivo, but exhibited a similar trend of PLGA degradation. Moreover, the internal structural evolution visually demonstrated these release behaviors. We selected for further examination the microsphere prepared by solvent evaporation because of its constant release rate, and explored its pharmacodynamics, histology, etc., in more detail. This microsphere when injected once showed equivalent efficacy to that of twice-daily injections of exenatide with no inflammatory response.

Stabilizing RNA by the sonochemical formation of RNA nanospheres

Biological macromolecules, including DNA, RNA, and proteins, have intrinsic features that make them potential building blocks for the bottom-up fabrication of nanodevices. Unlike DNA, RNA is a more versatile molecule whose range in the cell is from 21 to thousands of nucleotides and is usually folded into stem and loop structures. RNA is unique in nanoscale fabrication due to its diversity in size, function, and structure. Because gene expression analysis is becoming a clinical reality and there is a need to collect RNA in minute amounts from clinical samples, keeping the RNA intact is a growing challenge. RNA samples are notoriously difficult to handle because of their highly labile nature and tendency to degrade even under controlled RNase-free conditions and maintenance in the cold. Silencing the RNA that induces the RNA interference is viewed as the next generation of therapeutics. The stabilization and delivery of RNA to cells are the major concerns in making siRNAs usable drugs. For the first time, ultrasonic waves are shown to convert native RNA molecules to RNA nanospheres. The creation of the nanobubbles is performed by a one-step reaction. The RNA nanospheres are stable at room temperature for at least one month. Additionally, the nanospheres can be inserted into mammalian cancer cells (U2OS). This research achieves: 1) a solution to RNA storage; and 2) a way to convert RNA molecules to RNA particles. RNA nanosphere formation is a reversible process, and by using denaturing conditions, the RNA can be refolded into intact molecules.

Poly(D,L-lactide-co-glycolide) protein-loaded nanoparticles prepared by the double emulsion method—processing and formulation issues for enhanced entrapment efficiency

Although extensive research in the field of biodegradable microparticles containing peptide or protein drugs has greatly advanced production know-how, the effects of critical parameters influencing successful drug entrapment have not yet been sufficiently investigated with nano-scaled carriers. This paper deals with the formulation and processing parameters of the w(1)/o/w(2) double emulsion method that can affect nanoparticle size and loading. Fluorescein isothiocyanate-labelled bovine serum albumin (FITC-BSA) was used as a model protein. Results showed that high FITC-BSA entrapment efficiencies were reached (>80%) when sonication was used for the two emulsification steps of the nanoparticle formation, independently of the mixing durations and intensities. By comparison, the use of a vortex mixer for obtaining the primary w(1)/o emulsion led to a rather poor entrapment efficiency (approximately 25%). Some inherent properties of the poly(D,L-lactic-co-glycolic acid) polymer, such as, for example, high molecular weight, high hydrophilicity or the presence of free carboxylic end groups, enhanced the drug entrapment efficiency. It was also demonstrated that a low nominal drug loading, a large volume of the inner w1 phase or the choice of methylene chloride instead of ethyl acetate as organic solvent favoured the drug entrapment, with entrapment efficiency values often reaching 100%. However, when using methylene chloride, the mean particle size was substantially increased, due to the presence of larger particles. Mean particle size increased also when the polymer concentration in the organic phase was increased.

Effects of polymer, organic solvent and mixing strength on integrity of proteins and liposomes encapsulated in polymeric microspheres fabricated by the double emulsion process

The double emulsion process has commonly been applied to encapsulate water-soluble bioactive agents into polymeric microspheres. However, the integrity of many of these agents may be destroyed by the highly energetic procedures such as sonication that are routinely used to produce stable water-in-oil (w/o) emulsion. The aim of this research was to pursue the possibility of replacing the sonication by a mild emulsification procedure such as vortex mixing, with the use of certain materials to help to obtain stable w/o emulsion. The following materials were examined: poly(lactide-co-ethylene glycol) (PELA) as the polymer, ethyl acetate and acetone as the solvents, poly(vinyl alcohol) (PVA) and d-alpha tocopheryl polyethylene glycol 1000 succinate (Vitamin E TPGS) as the emulsifiers in w/o emulsion. The experimental results, with human serum albumin (HSA) as the encapsulated agent, showed that, when vortex mixing was used, these materials could significantly improve w/o emulsion stability and help to obtain satisfactory encapsulation effects, i.e. high encapsulation efficiency (EE) and low initial release burst. A delicate structure, i.e. liposomes, which is very sensitive to sonication, was then incorporated into microspheres by the 'modified double emulsion process'. It was found that the liposomes were intact and the encapsulation effects were good. Therefore, it can be concluded that the modified double emulsion process could be advantageous for the encapsulation of delicate substances.

Some basic parameters of microspheres fabricated from a branched oligoester by a rapid procedure

Microspheres were prepared from a branched copolymer of DL-lactic acid with mannitol containing native albumin and albumin labelled with fluorescein isothiocyanate, using a rapid method of distribution of methylformate as the solvent of the copolymer from the intermediate phase of the multiple w/o/w emulsion. The primary w/o emulsion was prepared by the method of homogenization with a turbine or, alternatively, by the method of dispersion with ultrasound in modified vessels. Different additives in the external aqueous phase, such as polyvinyl alcohol or the gelatin hydrolyzate as emulsifiers were tested. Ammonium sulphate, methylformate or ethyl acetate were used as moderators of solidification of microspheres. The effect of these selected formulation parameters on the size, encapsulation efficiency, yield of microspheres and on the course of the BSA and FITC-BSA release in vitro conditions were examined.

Control of encapsulation efficiency and initial burst in polymeric microparticle systems

Initial burst is one of the major challenges in protein-encapsulated microparticle systems. Since protein release during the initial stage depends mostly on the diffusional escape of the protein, major approaches to prevent the initial burst have focused on efficient encapsulation of the protein within the microparticles. For this reason, control of encapsulation efficiency and the extent of initial burst are based on common formulation parameters. The present article provides a literature review of the formulation parameters that are known to influence the two properties in the emulsion-solvent evaporation/extraction method. Physical and chemical properties of encapsulating polymers, solvent systems, polymer-drug interactions, and properties of the continuous phase are some of the influential variables. Most parameters affect encapsulation efficiency and initial burst by modifying solidification rate of the dispersed phase. In order to prevent many unfavorable events such as pore formation, drug loss, and drug migration that occur while the dispersed phase is in the semi-solid state, it is important to understand and optimize these variables.

Albumin loaded microsphere of amphiphilic poly(ethylene glycol)/ poly(α-ester) multiblock copolymer

The purpose of this study is to investigate the microspheres (MS) based on (AB)(n) type amphiphilic multiblock copolymers for sustained and complete release of a model protein, bovine serum albumin (BSA). The MS were prepared by a modified water-in-oil-in-water (W/O/W) double emulsion method using amphiphilic multiblock copolymers consisting of poly(ethylene glycol) (PEG) and a poly(alpha-ester), poly(epsilon-caprolactone) (PCL) or poly(l-lactic acid) (PLLA). The size of MS and encapsulation efficiency of BSA within MS were not noticeably influenced by the copolymer composition used in this experiment. While BSA was completely released from PEG/PLLA MS through matrix erosion and the diffusion of BSA, it was released only to an extent of 60% from PEG/PCL MS solely through the diffusion process. However, the release of BSA from PEG/PCL MS dramatically increased and then reached 100% release in 10 days after thermal treatment of the MS at 50 degrees C for 30 min in the middle of release test (on day 15).

Poly-epsilon-caprolactone microspheres and nanospheres: an overview

Poly-epsilon-caprolactone (PCL) is a biodegradable, biocompatible and semicrystalline polymer having a very low glass transition temperature. Due to its slow degradation, PCL is ideally suitable for long-term delivery extending over a period of more than one year. This has led to its application in the preparation of different delivery systems in the form of microspheres, nanospheres and implants. Various categories of drugs have been encapsulated in PCL for targeted drug delivery and for controlled drug release. Microspheres of PCL either alone or of PCL copolymers have been prepared to obtain the drug release characteristics. This article reviews the advancements made in PCL-based microspheres and nanospheres with special reference to the method of preparation of these and their suitability in developing effective delivery systems.

Mechanistic evaluation of the glucose-induced reduction in initial burst release of octreotide acetate from poly(d,l-lactide-co-glycolide) microspheres

One major obstacle for development of injectable biodegradable microspheres for controlled peptide and protein delivery is the high initial burst of drug release occurring over the first day of incubation. We describe here the significant reduction in initial burst release of a highly water-soluble model peptide, octreotide acetate, from poly(D,L-lactide-co-glycolide) microspheres by the co-encapsulation of a small amount of glucose (e.g., 0.2%w/w), i.e., from 30+/-20% burst - glucose to 8+/-3% + glucose (mean+/-SD, n=4). This reduction is unexpected since hydrophilic additives are known to increase porosity of microspheres, causing an increase in permeability to mass transport and a higher burst. Using the double emulsion-solvent evaporation method of encapsulation, the effect of glucose on initial burst in an acetate buffer pH 4 was found to depend on polymer concentration, discontinuous phase/continuous phase ratio, and glucose content. Extensive characterization studies were performed on two microsphere batches, +/-0.2% glucose, to elucidate the mechanism of this effect. However, no significant difference was observed with respect to specific surface area, porosity, internal and external morphology and drug distribution. Continuous monitoring of the first 24-h release of octreotide acetate from these two batches disclosed that even though their starting release rates were close, the microspheres + glucose exhibited a much lower release rate between 0.2 and 24h compared to those - glucose. The microspheres + glucose showed a denser periphery and a reduced water uptake at the end of 24-h release, indicating decreased permeability. However, this effect at times was offset as glucose content was further increased to 1%, causing an increase in surface area and porosity. In summary, we conclude that the effect of glucose on initial burst are determined by two factors: (1) increased initial burst due to increased osmotic pressure during encapsulation and drug release, and (2) decreased initial burst due to decreased permeability of microspheres.

Sonication parameters for the preparation of biodegradable nanocapsules of controlled size by the double emulsion method

The main goal of the present work was to study the influence of the sonication process on the characteristics of poly(lactide-co-glycolide) nanocapsules prepared by the water-in-oil-in-water solvent evaporation method. The duration and intensity of sonication were investigated with respect to their ability to modify the size and distribution of the nanocapsule population. It has been demonstrated that the duration of the second mixing step (leading to the w/o/w emulsion) is of greater influence than that of the first step (water-in-oil emulsion) on the final mean particle size. A three-dimensional response surface was drawn up to show that when the second emulsification time increased, the mean size decreased until reaching a plateau. A threshold in sonication intensity also exists, allowing optimization of both parameters and the formation of nanocapsules of controlled size with a rather narrow distribution. The use of a vortex mixer instead of a sonicator during the first mixing step led to nanocapsules with a similar response surface, supporting the idea that the second step is the decisive one. Finally, nanocapsules loaded with methylene blue, a hydrophilic model compound with a positive charge, were characterized and the encapsulation efficiency calculated. Their size and distribution were similar to that of the blank nanocapsules. Entrapment efficiency was independent of duration, intensity, and type of mixing. From these results, it was concluded that nanocapsules of controlled size could be obtained upon optimizing certain process parameters.

A comparative biocompatibility study of microspheres based on crosslinked dextran or poly(lactic-co-glycolic)acid after subcutaneous injection in rats

Microspheres based on methacrylated dextran (dex-MA), dextran derivatized with lactate-hydroxyethyl methacrylate (dex-lactate-HEMA) or derivatized with HEMA (dex-HEMA) were prepared. The microspheres were injected subcutaneously in rats and the effect of the particle size and network characteristics [initial water content and degree of methacrylate substitution (DS)] on the tissue reaction was investigated for 6 weeks. As a control, poly(lactic-co-glycolic)acid (PLGA) microspheres with varying sizes (unsized, smaller than 10 microm, smaller and larger than 20 microm) were injected as well. A mild tissue reaction to the PLGA microspheres was observed, characterized by infiltration of macrophages (MØs) and some granulocytes. Six weeks postinjection, the PLGA microspheres were still present. However, their size was decreased indicating degradation and many spheres had been phagocytosed. The tissue reaction was hardly affected by size differences, except for particles smaller than 10 microm, which induced an extensive tissue reaction. The initial tissue reaction to nondegradable dex-MA microspheres was stronger than towards the PLGA microspheres, but at day 10 the tissue reactions were comparable for both groups. Six weeks postinjection, the dex-MA microspheres were completely phagocytosed, and no signs of degradation were observed. The size and initial water content of dex-MA microspheres hardly affected the tissue response, although less granulocytes were observed for microspheres with higher DS. Slowly degrading dextran microspheres composed of dex-(lactate(1)-)HEMA induced a tissue reaction comparable to the PLGA microspheres. However, degradation of the dex-(lactate(1,3)-)HEMA microspheres was associated with an increased number of MØ's and giant cells, both phagocytosing the microspheres and their degradation products. Similar to PLGA, no adverse reactions were observed for the nondegradable dex-MA and degradable dextran microspheres. This study shows that both nondegradable and degradable dextran-based microspheres are well tolerated after subcutaneous injection in rats, which make them interesting candidates as controlled drug delivery systems.

Fabrication of porous poly(epsilon-caprolactone) microparticles for protein release

The particle morphology and in vitro release of protein from porous and non-porous PCL-F127 blended microparticles were evaluated. The BSA loaded PCL microparticles were prepared by the w/o/o/o emulsion-solvent evaporation method. Two types of homogenizer, a Polytron homogenizer and a probe ultrasonicator, were used to prepare the emulsion systems. The effects of solvent evaporation rate on the crystallinity and the performance of the microparticles were investigated. Both microparticles showed quite different shapes as well as surface morphology and release characteristics. The microparticles prepared with a Polytron homogenizer were quite porous in structure, which created channels for protein to continuously diffuse out, and resulted in sustained- and controlled-release characteristics. In addition, the initial burst release of protein from the microparticles was also reduced. Alteration of the evaporation rate of solvent did not change the crystallinity of the final microparticles. An influence of evaporation rate on the size of resulting microparticles was observed. The porous PCL microparticles were developed by choosing a proper homogenizer and fabrication conditions. Carefully controlling these variables resulted in microparticles with desirable release performance.

Phase transfer and characterization of poly(epsilon-caprolactone) and poly(L-lactide) microspheres

A method suitable for transfer of poly(epsilon-caprolactone) and poly(L-lactide) microspheres (synthesized by pseudoanionic dispersion polymerization of epsilon-caprolactone and L-lactide in heptane-1,4-dioxane mixed solvent) from heptane to water was developed. This method consists of treating the microspheres with KOH-ethanol in the presence of surfactants (nonionic Triton X-405, anionic sodium dodecyl sulfate (SDS), and zwitterionic ammonium sulfobetaine-2 (ASB)). Partial hydrolysis of polyesters results in the formation of hydroxyl and carboxyl groups in the surface layer of microspheres and enhances their stability in water-based media. Minimal concentrations of surfactants, needed to obtain stable suspensions of particles, were equal to 3 x 10(-2) and 6 x 10(-2), and 3 x 10(-2) mol l(-1) for Triton X-405. SDS, and ASB, respectively. In the case of poly(epsilon-caprolactone) microspheres, suspensions in water were stable for all three surfactants for pH values ranging from 3 to 11. Suspensions of poly(L-lactide) were stable in the same range of pH values only for ASB. Surface charge density determined by electrophoretic mobility varied for poly(epsilon-caprolactone) microspheres from 2.6 x 10(-7) to 8.9 x 10(-7) mol m(-2), for particles stabilized with Triton X-405 and ASB. respectively. In the case of poly(L-lactide) microspheres, surface charge density varied from 3.9 x 10(-7) (stabilizer: Triton X-405) to 7.4 x 10(-7) mol m(-2) (stabilizer: ASB). Carboxyl groups located in the surface layer of poly(L-lactide) microspheres were used for covalent immobilization of 6-aminoquinoline, a fluorophore with an amino group. Maximum surface concentration of immobilized 6-aminoquinoline was equal to 1.9 x 10(-6) mol m(-2). Poly(epsilon-caprolactone) microspheres transferred into water were loaded with ethyl salicylate. Loading up to 38% (w/w) was obtained.

The manufacturing techniques of various drug loaded biodegradable poly(lactide-co-glycolide) (PLGA) devices

A considerable research has been conducted on drug delivery by biodegradable polymeric devices, following the entry of bioresorbable surgical sutures in the market about two decades ago. Amongst the different classes of biodegradable polymers, the thermoplastic aliphatic poly(esters) like poly(lactide) (PLA), poly(glycolide) (PGA), and especially the copolymer of lactide and glycolide, poly(lactide-co-glycolide) (PLGA) have generated immense interest due to their favorable properties such as good biocompatibility, biodegradability, and mechanical strength. Also, they are easy to formulate into different devices for carrying a variety of drug classes such as vaccines, peptides, proteins, and micromolecules. Also, they have been approved by the Food and Drug Administration (FDA) for drug delivery. This review discusses the various traditional and novel techniques (such as in situ microencapsulation) of preparing various drug loaded PLGA devices, with emphasis on preparing microparticles. Also, certain issues about other related biodegradable polyesters are discussed.

Microspheres for protein delivery prepared from amphiphilic multiblock copolymers. 1. Influence of preparation techniques on particle characteristics and protein delivery

The entrapment of lysozyme in amphiphilic multiblock copolymer microspheres by emulsification and subsequent solvent removal processes was studied. The copolymers are composed of hydrophilic poly(ethylene glycol) (PEG) blocks and hydrophobic poly(butylene terephthalate) (PBT) blocks. Direct solvent extraction from a water-in-oil (w/o) emulsion in ethanol or methanol did not result in the formation of microspheres, due to massive polymer precipitation caused by rapid solvent extraction in these non-solvents. In a second process, microspheres were first prepared by a water-in-oil-in-water (w/o/w) emulsion system with 4% poly(vinyl alcohol) (PVA) as stabilizer in the external phase, followed by extraction of the remaining solvent. As non-solvents ethanol, methanol and mixtures of methanol and water were employed. However, the use of alcohols in the extraction medium resulted in microspheres which gave an incomplete lysozyme release at a non-constant rate. Complete lysozyme release was obtained from microspheres prepared by an emulsification-solvent evaporation method in PBS containing poly(vinyl pyrrolidone) (PVP) or PVA as stabilizer. PVA was most effective in stabilizing the w/o/w emulsion. Perfectly spherical microspheres were produced, with high protein entrapment efficiencies. These microspheres released lysozyme at an almost constant rate for approximately 28 days. The reproducibility of the w/o/w emulsion process was demonstrated by comparing particle characteristics and release profiles of three batches, prepared under similar conditions.

Effects of salt addition on the microencapsulation of proteins using W/O/W double emulsion technique

The influence of co-encapsulation of stabilizing additives together with BSA on microsphere characteristics using the modified water-in-oil-in-water emulsion solvent evaporation (W/O/W) method was investigated. For this purpose, poly(L-lactide) microspheres containing bovine serum albumin (BSA) were prepared. The morphology, porosity, specific surface area, particle size, encapsulation efficiency and kinetics of drug release of protein loaded microspheres were analysed in relation to the influence of co-encapsulated stabilizing additives such as electrolytes. High salt concentrations in the internal (W1) aqueous phase, often necessary to stabilize protein or antigen solutions, led to an increase in particle size, particle size distribution, porosity and specific surface area. Bulk density and encapsulation efficiency decreased. The release profile was characterized by a high initial burst due to the highly porous structure. Addition of salt to the external or continuous water phase (W2), however, stabilized the encapsulation process and, therefore, resulted in improved microsphere characteristics as a dense morphology, a reduced initial burst release, a drastically increased bulk density and encapsulation efficiency. Analysis of the specific surface area (BET) showed that the addition of salt to W2, regardless of the salt concentration in the W1 phase, decreased the surface area of the microspheres approximately 23-fold. Microsphere properties were influenced by salts additions through the osmotic pressure gradients between the two aqueous phases and the water flux during microsphere formation. Release profiles and encapsulation efficiencies correlated well with the porosity and the surface area of microspheres. Furthermore, the influence of a low molecular weight drug and different time-points of salt addition to W2 on microsphere characteristics were studied by encapsulation of acid orange 63 (AO63), confirming the results obtained with BSA. This study suggests that modification of the external water phase by adding salts is a simple and efficient method to encapsulate stabilized protein solution, with high encapsulation efficiency and good microsphere characteristics.

Sustained release microspheres of metoclopramide using poly(D,L-lactide-co-glycolide) copolymers

Metoclopramide was encapsulated with poly(D,L-lactide co glycolide) copolymers of different molecular weights using the emulsification/solvent evaporation technique. These polymers included poly(D,L-lactide-co-glycolide) 50:50 with inherent viscosity (i.v.) 0.2, and average molecular weight 8000, poly(D,L-lactide-co-glycolide) 50:50 with i.v. 0.8 and average molecular weight 98000 and poly(D,L-lactide-co-glycolide) 85:15 with i.v. 1.4 and average molecular weight 220000. The effect of the polymers' molecular weights as well as the polymer-to-drug ratios on the yield, the particle size distribution, and the drug content of the microspheres was investigated. The release rate of the drug was studied for 96 h in a phosphate buffer of pH 7.4. The study also investigated the effect of the new poly(lactide-co-glycolide)-H series on the characteristics of the prepared microspheres. Data revealed that a higher yield was obtained with polymers of lower molecular weights. A lower yield was also obtained with increasing the drug-to-polymer ratios for all the investigated polymers. The drug content of the microspheres was lower than expected, ranging from 49-85%, which suggested a chemical interaction between the drug and the polymers, as proved by differential scanning calorimetry (DSC) and infra red (IR) studies. A higher interaction was obtained with the H-series of the copolymers. The release of the drug mainly followed zero order kinetics on increasing either the polymers' molecular weights or the polymer-to-drug ratios. Diffusion kinetics was observed only with those batches prepared with low polymer-to-drug ratios. The release rate was a function of both the polymers' molecular weights and the drug-to-polymer ratios.

Formulation of poly(D,L-lactic-co-glycolic acid) microparticles for rapid plasmid DNA delivery

An optimised water-in-oil-in-water double emulsion process for the microencapsulation of plasmid DNA in poly(D,L-lactic-co-glycolic acid) (PLGA) was used to prepare microparticles from a range of different PLGA formulations. This process has been developed using pharmaceutically accepted solvents and is potentially scaleable. Incorporation of plasmid DNA in the microparticles of up to 11 microg/mg was obtained and the retention of plasmid DNA integrity was considerably greater than previously reported. Microparticle structure was determined, by scanning electron microscopy, to be hollow and size distribution characteristics were found to be independent of polymer formulation. The ability to vary the plasmid DNA release profile by changing the PLGA formulation and polymer concentration used in the encapsulation process was also demonstrated. This ability to control the release profile of the microparticles was shown to be especially important as the physical integrity of the encapsulated plasmid DNA was found to deteriorate with extended release times in vitro.

Biodegradable recombinant human erythropoietin loaded microspheres prepared from linear and star-branched block copolymers: influence of encapsulation technique and polymer composition on particle characteristics

Recombinant human erythropoietin (EPO) and fluorescein isothiocyanate labeled dextran (FITC-dextran) loaded microspheres were prepared by a modified W/O/W double-emulsion technique. Biodegradable linear ABA block copolymers consisting of poly(L-lactide-co-glycolide) A blocks attached to central poly(ethyleneoxide) (PEO) B blocks and star-branched AB block copolymers containing A blocks of poly(L-lactide) or poly(L-lactide-co-glycolide) and star-branched poly(ethyleneoxide) B blocks were investigated for their potential as sustained release drug delivery systems. Microsphere characteristics were strongly influenced by the polymer composition. In the case of the linear block copolymers, a reduced lactic acid content in a linear block copolymer yielded smaller particles, a lower encapsulation efficiency, and a higher initial drug release both in the case of EPO and FITC-dextran. The investigation of the effects of several manufacturing parameters on microsphere formation showed that the process temperature plays an important role. Microsphere formation in a +1 degrees C environment resulted in higher drug loadings without increasing the amount of residual dichloromethane inside the particles. Other parameters such as the homogenization of the primary W/O emulsion and of the W/O/W double-emulsion have less impact on microsphere characteristics. Branched block copolymers containing star-shaped PEO also showed potential for the preparation of drug loaded microspheres. A certain amount of glycolic acid in the copolymer was necessary for the successful preparation of non-aggregating microspheres at room temperature. Again, the processing temperature strongly affected particle characteristics. Microsphere preparation at +1 degrees C allows the formation of microspheres from a polymer not containing glycolic acid, a result which could not be achieved at room temperature. Moreover, compared to microsphere formation at room temperature, the effective FITC-dextran loading was increased. Concerning the EPO loaded microspheres, the amount of EPO aggregated was comparable to that using the linear ABA polymers. A continuous release of the protein from these star-shaped polymers could not be achieved. In conclusion, apart from microsphere preparation in a +1 degrees C environment the choice of the polymer represents the main factor for a successful entrapment of proteins into biodegradable microspheres.

Performance of sonication and microfluidization for liquid-liquid emulsification

The purpose of this research was to evaluate and compare liquid-liquid emulsions (water-in-oil and oil-in-water) prepared using sonication and microfluidization. Liquid-liquid emulsions were characterized on the basis of emulsion droplet size determined using a laser-based particle size analyzer. An ultrasonic-driven benchtop sonicator and an air-driven microfluidizer were used for emulsification. Sonication generated emulsions through ultrasound-driven mechanical vibrations, which caused cavitation. The force associated with implosion of vapor bubbles caused emulsion size reduction and the flow of the bubbles resulted in mixing. An increase in viscosity of the dispersion phase improved the sonicator's emulsification capability, but an increase in the viscosity of the dispersed phase decreased the sonicator's emulsification capability. Although sonication might be comparable to homogenization in terms of emulsification efficiency, homogenization was relatively more effective in emulsifying more viscous solutions. Microfluidization, which used a high pressure to force the fluid into microchannels of a special configuration and initiated emulsification via a combined mechanism of cavitation, shear, and impact, exhibited excellent emulsification efficiency. Of the three methodologies, sonication generated more heat and might be less suitable for emulsion systems involving heat-sensitive materials. Homogenization is in general a more effective liquid-liquid emulsification method. The results derived from this study can serve as a basis for the evaluation of large-scale liquid-liquid emulsification in the microencapsulation process.

Protein encapsulation in biodegradable amphiphilic microspheres

MPOE-PLA microspheres containing bovine serum albumin (BSA) were prepared by the double emulsion method with high encapsulation efficiency ( approximately 93%). Confocal scanning microscopic analysis using MPOE-PLA labelled with 1-pyrenemethanol showed the MPOE coating of the microsphere surface. This coating improves the performance of the release system compared with PLA microspheres; the hydrophilic chains reduce the BSA adsorption onto the microspheres and increase the amount of BSA released in the supernatant. Microsphere analysis using atomic force microscopy showed that the presence of the MPOE chains also leads to surface roughness. Studies of the diffusion of 1% rhodamine aqueous solution into the microspheres by means of confocal microscopy showed a fast diffusion of water through the matrices containing high molecular weight MPOE chains (?10 000 g mol-1) and could explain the fast release of BSA from these microspheres.

A polysorbate-based non-ionic surfactant can modulate loading and release of beta-lactoglobulin entrapped in multiphase poly(DL-lactide-co-glycolide) microspheres

PURPOSE

The goal of the present paper was to investigate the role of a surfactant, Tween 20, in the modulation of the entrapment and release of beta-lactoglobulin (BLG) from poly (DL-lactide-co-glycolide) microspheres.

METHODS

Poly(DL-lactide-co-glycolide) microspheres containing BLG were prepared by a water-in-oil-in-water emulsion solvent procedure. Tween 20 was used as a surfactant in the internal aqueous phase of the primary emulsion. BLG entrapment efficiency and burst release were determined. Displacement of BLG from microsphere surface was followed by confocal microscopy observations and zeta potential measurements, whereas morphological changes were observed by freeze-fracture electron microscopy.

RESULTS

Tween 20 was shown to increase 2.8 fold the encapsulation efficiency of BLG without any modification of the stability of the first emulsion and the viscosity of the internal aqueous phase. In fact, Tween 20 was shown to be responsible for removing the BLG molecules that were adsorbed on the particle surface or very close to the surface as shown by confocal microscopy and zeta potential measurements. Tween 20 reduced the number of aqueous channels between the internal aqueous droplets as well as those communications with the external medium. Thus, the more dense structure of BLG microspheres could explain the decrease of the burst release.

CONCLUSIONS

These results constitute a step forward in the improvement of existing technology in controlling protein encapsulation and delivery from microspheres prepared by the multiple emulsion solvent evaporation method.

Degradation and release profile of microcapsules made of poly[L-lactic acid-co-L-lysine(Z)]

Poly(L-lactic acid-co-L-lysine(Z)) with different Lys(Z) contents was synthesized by Sn(II) salt-catalyzed ring-opening copolymerization of 3(S)-benzyloxycarbonylaminobutyl-6(S)-methylmorpholine-2,5-dione with lactide. Microcapsules of the copolymers were prepared by solvent evaporation from w/o/w emulsion, and FITC-dextran release from the microcapsules was investigated. The FITC-dextran release was dependent on the composition and molecular weight of the copolymers. The release from the microcapsules containing Lys(Z) of 6.5 mol% was slowest among the present microcapsules, which is due to smooth surface and very small microcapsules included in a large microcapsule. On the other hand, the release from microcapsules containing Lys(Z) of 31 or 50 mol% became faster after several days of incubation. GPC measurement of the microcapsules revealed that the copolymers were degraded during the incubation. Cracks and pores were formed on the microcapsule wall. PLLA microcapsules having comparable molecular weight to the copolymers showed neither release acceleration nor degradation in short-time incubation. Therefore, the introduction of Lys(Z) units made PLLA susceptible to degradation to result in delayed acceleration of release.

Controlled drug delivery by biodegradable poly(ester) devices: different preparative approaches

There has been extensive research on drug delivery by biodegradable polymeric devices since bioresorbable surgical sutures entered the market two decades ago. Among the different classes of biodegradable polymers, the thermoplastic aliphatic poly(esters) such as poly(lactide) (PLA), poly(glycolide) (PGA), and especially the copolymer of lactide and glycolide referred to as poly(lactide-co-glycolide) (PLGA) have generated tremendous interest because of their excellent biocompatibility, biodegradability, and mechanical strength. They are easy to formulate into various devices for carrying a variety of drug classes such as vaccines, peptides, proteins, and micromolecules. Most importantly, they have been approved by the United States Food and Drug Administration (FDA) for drug delivery. This review presents different preparation techniques of various drug-loaded PLGA devices, with special emphasis on preparing microparticles. Certain issues about other related biodegradable polyesters are discussed.

Changing the pH of the external aqueous phase may modulate protein entrapment and delivery from poly(lactide-co-glycolide) microspheres prepared by a w/o/w solvent evaporation method

The milk model protein, beta lactoglobulin (BLG), was encapsulated into microspheres prepared by a multiple emulsion/solvent evaporation method. The effect of the pH of the outer aqueous phase on protein encapsulation and release as well as on microsphere morphology has been investigated. At all tested pH values, the encapsulation efficiency was shown to decrease with increasing the initial amount of BLG. This was correlated with the reduced stability of the primary emulsion as the initial BLG increased. In addition, reducing the solubility of BLG in the external aqueous phase by decreasing the pH to the isoelectric point of BLG (pI 5.2) resulted in an improved protein encapsulation. Moreover, it was shown that combining pH modification and optimal stability of the first emulsion yielded microspheres with a high encapsulation efficiency. However, release kinetic studies revealed that a significant burst release was observed with microspheres loaded with large amounts of BLG, especially when prepared in a medium at pH 5.2. This burst effect was attributed to morphology changes in the microsphere surface which was characterized by the presence of pores or channels able to accelerate the release of BLG. These pores were assumed to result from the presence of large amounts of protein molecules on the microsphere surface, that aggregate during microsphere formation at pH 5.2. Indeed, single adsorption experiments have shown that BLG had a higher affinity for the particle surface when the pH was close to the pI. Thus, reducing the solubility of a protein in the external aqueous phase allows the product of microspheres with a better encapsulation efficiency, although this benefit is provided by a strong adsorption of the protein on microsphere surface.

Bovine serum albumin loaded poly(lactide-co-glycolide) microspheres: the influence of polymer purity on particle characteristics

To study the influence of polymer purity on microsphere characteristics, bovine serum albumin (BSA) loaded biodegradable microspheres were prepared by spray drying using two samples of poly(lactide-co-glycolide), PLG, (50:50, mwt = 35 and 69 kDa). Polymer properties were varied by DL-lactide and glycolide addition or by ultrafiltration. While the effective drug loading was not affected by polymer purity, Tg was decreased with increasing monomer and oligomer content. The removal of these low molecular weight substances by ultrafiltration led to a narrower molecular weight distribution compared to the untreated PLG. Concerning the polymer with the higher molecular weight, microsphere morphology was also strongly affected by polymer composition. In contrast to the non-modified PLG, monomer addition yielded particles with a much smoother surface structure. Moreover, in vitro cytotoxicity of the microspheres prepared from the polymer pretreated by ultrafiltration was significantly reduced, whereas monomer addition caused a dramatic decrease of cells surviving contact with the microsphere extract. The in vivo degradation rate of the ultrafiltered microspheres was decreased and as a result, protein release at later times was slowed down. Furthermore, depending on the effective drug loading level, monomer addition resulted in a decrease in the initial protein burst. It can be concluded that the effect of low molecular weight impurities in a polymer on microsphere characteristics and on cytotoxicity cannot be ignored. Their elimination is possible by ultrafiltration.

Recombinant human erythropoietin (rhEPO) loaded poly(lactide-co-glycolide) microspheres: influence of the encapsulation technique and polymer purity on microsphere characteristics

Recombinant human erythropoietin (EPO) and fluorescein isothiocyanate-labelled dextran (FITC-dextran) loaded biodegradable microspheres were prepared from poly(lactide-co-glycolide) (PLG) by a modified spray-drying technique. This microencapsulation method was compared with the water-in-oil-in-water (w/o/w) double-emulsion method. As expected, microsphere morphology, particle size and particle size distribution strongly depended on the production process. The spray-drying method was found to have a number of advantages compared to the w/o/w double-emulsion technique. The content of residual dichloromethane (DCM) in the final product was significantly lower in case of the microspheres prepared by spray-drying. Concerning EPO loaded microspheres, spray-drying yielded higher encapsulation efficiencies. Although the microspheres obtained by spray-drying are subjected to intensive mechanical and thermal stress during the preparation, the amount of aggregates of EPO in PLG microspheres were not increased compared to the w/o/w technique. Depending on the manufacturing method, addition of cyclic DL-lactide dimers (referred to as monomers in the following) affected the in vitro release profiles of EPO and FITC-dextran from PLG microspheres. Using differential scanning calorimetry it was shown that these low molecular weight substances only seem to be present inside the microspheres produced by spray-drying. DL-Lactide significantly reduced the initial burst release of both EPO and FITC-dextran. While the following release period of EPO was not affected by the DL-lactide content, a more linear FITC-dextran release pattern could be achieved. It can be concluded that the spray-drying technique provides a number of advantages compared to the w/o/w method. The modulation of protein release using low molecular weight additives is of particular interest for parenteral depot systems.

Ultrasound-induced degradation of PLA and PLGA during microsphere processing: influence of formulation variables

The effect of probe sonication during microsphere processing on the stability of various aliphatic polyesters based on lactic acid (PLA) and lactic/glycolic acid (PLGA) was investigated. The weight average molecular weight (Mw) of the polymers dissolved in dichloromethane (DCM) generally decreased with an increase in duration and/or intensity of the sonication process. The extent of the Mw-reduction was more pronounced with polymers of high initial Mw and high GA content. Polydispersity indices (PD=Mw/Mn) were nearly unchanged indicating that random chain cleavage is the likely degradation mechanism. From the observation that ultrasound-induced polymer degradation slightly increased in the presence of suspended drug particles acting as cavitation nuclei, it can be concluded that the mechanical stress induced by the implosive collapse of cavitation bubbles is at least partly responsible for the observed effects in PLA/ PLGA solutions. The use of ultrasound for the preparation of W/O, O/W and W/O/W emulsions exhibited different effects depending on the formulation and the type of emulsion. The preparation of W/O emulsions generally lead to Mw-changes comparable to those observed for the corresponding polymer solutions. Fatty acid free bovine serum albumin (BSAff) was found to protect PLA and PLGA against ultrasound-induced degradation in W/O-emulsions due to the formation of a semisolid interfacial film. A tremendous effect not only on the polymer Mw, but also on its PD could be observed, when ultrasound was used to emulsify an organic polymer solution or W/O-emulsion in an external aqueous phase. As this last finding was found to have rather important implications on the drug loading efficiency, the hydration, the degradation and the initial release characteristics of the resulting microspheres, it can be concluded that probe sonication can be a rather critical process step during the preparation of microspheres.

A new strategy to determine the actual protein content of poly(lactide-co-glycolide) microspheres

Bovine serum albumin, lysozyme, and trypsin inhibitor were first encapsulated into poly-d,l-lactide-co-glycolide (PLGA) microspheres and then a new strategy was used to quantitate the actual levels of proteins in the microspheres. The proper combination of water-miscible dimethyl sulfoxide and 0.05 N-NaOH containing 0.5% sodium dodecyl sulfate (SDS) made it possible to solubilize both PLGA microspheres and proteins in a single phase. A total protein assay conveniently provided accurate information on the amount of protein encapsulated into the microspheres. In contrast to conventional techniques making use of acetonitrile, dichloromethane, and SDS extraction methods, this new method did not necessitate polymer precipitation, filtration, and protein extraction into other phases. These features were a great advantage in recovering proteins without any loss due to experimental processes. As a consequence, the new method reported in this study provided accurate data for the actual level of protein in PLGA microspheres, regardless of the pattern of protein distribution inside microspheres or the characteristics of microspheres. The experiment relying on the use of a radiolabeled protein also validated the reliability of this new method.

Injectable microcapsules prepared with biodegradable poly(alpha-hydroxy) acids for prolonged release of drugs

In this paper, microencapsulation techniques for the preparation of drug-containing monolithic microcapsules for prolonged release using biodegradable poly(alpha-hydroxy) acids, such as polylactic acid, poly(lactide-co-glycolide) and copoly(lactic/glycolic) acid are reviewed. Phase separation, solvent evaporation, and spray drying procedures are discussed. In order to achieve controlled-release formulations of highly water-soluble drugs that are entrapped efficiently, various manufacturing techniques and procedures have been developed. Degradation of poly(alpha-hydroxy) acids is altered by the copolymer ratio and molecular weight of the polymer used to make microcapsules and the amounts of released microencapsulated drugs correlate almost linearly with polymer degradation, indicating that controlled-release formulations, which release drugs over different times, can be prepared using suitable poly(alpha-hydroxy) acids with different degradation rates.

Dual-controlled drug delivery across biodegradable copolymer. I. Delivery kinetics of levonorgestrel and estradiol through (caprolactone/lactide) block copolymer

Four block copolymers of caprolactone (CL) and dl-lactide (LA) with varying weight fractions were synthesized by living polymerization in the presence of Al/Zn bimetallic alkoxide complex. The solubility of levonorgestrel (LNG) and estradiol (E2) in the copolymers was evaluated and found to increase exponentially with CL mole fraction. Their aqueous solubilities were also studied and observed to increase linearly with the concentration of benzalkonium chloride (BAC), a solubilizer. The kinetics of LNG and E2 permeation through the copolymer membranes were studied and observed to follow a zero-order kinetics, and the permeation rates obtained were noted to be a function of copolymer composition. The release kinetics through the copolymer matrix were also studied and noted to follow a matrix-diffusion process, and the release flux was found to be dependent on copolymer composition. Permeation rates and release fluxes at steady state as well as the permeability and solubility of LNG and E2 in the copolymers suggest that these permeation parameters are affected by copolymer composition, which increase as the CL/LA ratio in the copolymer was increased.